The invention relates to a cylinder for receiving a printing form, in particular for receiving a printing film for offset printing.
Heretofore known printing form cylinders have systems therewithin for winding printing film onto reels or spools and for unwinding the printing film therefrom. Starting from the wind-up reel, the film is guided outwardly through a slit-like gap. The film is looped around the outer or jacket surface of the cylinder and is led back through the same gap or another gap into the interior of the cylinder and onto the wind-up reel. In this regard, an effort is made to apply tension to or tauten the film uniformly on the cylinder, for which purpose high tension forces take effect in order to overcome the friction between the film underside and the jacket surface (note German Patent 27 56 388 and published German Patent Documents DE 42 24 332 A1 and DE 43 29 125 C1).
A disadvantage of the heretofore known procedures is that, despite high tension forces, the film is seated movably on the jacket surface of the printing form cylinder. This results, during printing, in wearing of the film and in printing errors.
It is accordingly an object of the invention to provide a cylinder for receiving a printing form which, at relatively little outlay, allows a printing form to be tautened uniformly and without any movement.
With the foregoing and other objects in view, there is provided, in accordance with the invention, a cylinder for receiving a printing form, the cylinder being formed with a gap having gap edges, which projects into the interior of the cylinder, the gap extending in a direction of generatrices of the cylinder and serving for guiding ends of a printing form therethrough, comprising a device for tautening the printing form on a jacket surface of the cylinder, at least one of the gap edges having a curvature for attaining tensioning forces which are constant over at least approximately the entire width of the printing form.
In accordance with another feature of the invention, the curvature, in the circumferential direction of the cylinder, projects in the region of the center of the printing form and recedes in side regions of the printing form.
In accordance with a further feature of the invention, the tautening device acts at both ends of the printing form, both of the gap edges having a cambered form, and being spaced apart a distance is reduced in the region of the center of the printing form, and increases continuously towards side regions of the printing form.
In accordance with an added feature of the invention, the gap edges are rounded.
In accordance with an additional feature of the invention, the gap edges have a low coefficient of friction.
In accordance with a concomitant feature of the invention, the cylinder includes roller elements for at least partly carrying the printing form, the roller elements serving for reducing the friction along the curved gap edges.
Due to the curved form of at least one of the gap edges of a cylinder, it is possible to mount a printing form, in particular a printing film, in tension on the outer or jacket surface of the cylinder, so that there is substantially uniform tension in the printing form over the width thereof.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a cylinder for receiving a printing form, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings, wherein: